This invention relates to an axial pin tumbler lock cooperative with a cylindrical key and capable of having tumbler combination changes by means of various set keys while normal lock operation is effected by means of an appropriate service key.
Vending machines require periodic service to collect revenues, resupply vended articles and the like. Typically a series of such machines include locks which are identical and which are operated by the same, identical service key. Thus a service man or revenue collector will use the single key for servicing a number of separate machines.
In order to maintain security for such machines, one must often change the locks or alternatively change the combination for the locks incorporated with such machines. Changing vending machine locks is time consuming and costly. Consequently, various locks have been developed that incorporate a mechanism rendering such locks capable of having their combination changed. The combinations are generally changed by re-arranging the tumblers within the locking mechanism for the lock.
Numerous prior art patents disclose means for changing the tumbler combination of a lock. Among these prior art patents are the following: Schlage, U.S. Pat. No. 3,411,331, Axial Pin Cylinder Device, issued Nov. 19, 1968; Monahan, U.S. Pat. No. 3,422,646, Instantaneous Tumbler Change Lock, issued Jan. 21, 1969; Christopher, U.S. Pat. No. 3,102,412, Tumbler Lock with Axially Shiftable Interchangeable Tumblers, issued Sept. 3, 1963; Kerr, U.S. Pat. No. 3,261,188, Quick Change Axial Pin Tumbler Lock Assembly, issued July 15, 1966; Pepper, U.S. Pat. No. 1,707,922, Lock, issued Apr. 2, 1929; Best, U.S. Pat. No. 3,206,958, Interchangeable Lock Cores, issued Sept. 21, 1965; Kerr, U.S. Pat. No. 3,251,205, Quick Change Axial Pin Tumbler Lock Assembly, issued May 17, 1966; Kerr, U.S. Pat. No. 3,258,944, Assembly Jig for Facilitating Lock Tumbler Changeover Operations, issued July 5, 1966; Faulk, U.S. Pat. No. 3,728,880, Rekeyable Axial Pin Tumbler Lock, issued Apr. 24, 1973; Faulk, U.S. Pat. No. 3,738,136, System for Master Key and Axial Pin Tumbler Locks, issued June 12, 1973; and Walters and Brattland, U.S. Pat. No. 3,648,492 for Pin Tumbler Lock and Key Structure issued Mar. 14, 1972.
The referenced patents disclose various types of pin tumbler locks which may have their combinations altered by various means. Some disclose a cylindrical key having circumferential detents. The key is received in an annular opening of a lock where it engages a radial array of axial pin tumblers and depresses those pin tumblers to an appropriate depth within a barrel cylinder to permit rotation of a plug with respect to a cylinder over a shear interface. Some references disclose one shear interface while others disclose multiple shear interfaces. In references disclosing a single interface construction, various arrangements are disclosed for mechanically altering the pin tumbler configuration within the lock barrel to thereby change the combination of the device.
Other references disclose multiple rotating barrel and plug members with additional pin tumblers stored in one of the members. Movement of pin tumblers is then effected across two or more shear interfaces in order to vary the lock combination. Monahan U.S. Pat. No. 3,422,646 discloses such a configuration.
While such prior art lock devices are useful, they are quite complex and require precision manufacture. As a result, a simplified changeable key lock construction is desirable. Moreover, it is desired that such a lock construction be compatible with keys of the type currently available in the marketplace including keys such as the cylindrical key described in Walters et al, U.S. Pat. No. 3,648,492. These considerations, among others, inspired the development of the present invention.